• Journal of the Society of Naval Architects of Korea
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• v.60 no.3
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• pp.146-154
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• 2023

Efforts have been made to reduce the greenhouse gas emissions from ships by limiting the energy efficiency index, and net zero CO₂ emission was proposed recently. The most ideal measure to achieve zero emission ship is electrification, and fuel cells are considered as a practical power source of the electrified propulsion system. The electric efficiency in the electrochemical reaction of fuel cells can be achieved up to 60% practically. The remaining energy is converted to heat energy but most of them are dissipated by cooling. In the author's previous research, a hybrid propulsion system utilizing not only electricity but also heat was introduced by combining electric motor and steam turbine. In this article, long term efficiency is evaluated for the introduced hybrid propulsion system by considering a virtual 24,000 TEU class container carrier model. To reflect a more practical operating condition, the actual navigation data of a similar real ship in the real world were collected from automatic identification system data and applied. From the result, the overall efficiency of the hybrid propulsion system is expected to be higher than a conventional electric propulsion fuel cell ship by 30%.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.183-188
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• 2017

This paper provides numerical results for the estimation of the efficiency of KRISO energy saving devices in the design stage. A finite volume method is used to solve Reynolds averaged Navier-Stokes (RANS) equations, where the SST k-$\omega$ model is selected for turbulence closure. The propeller rotating motion is determined using a rigid body motion (RBM) scheme, which is called a sliding mesh technique. The numerical analysis focuses on predicting the power reduction by the designed KRISO devices (K-DUCT) under a self-propulsion condition. The present numerical results show good agreement with the available experimental data. Finally, it is concluded that CFD can be a useful method, along with model tests, for assessing the performance of energy saving devices for propulsion efficiency improvement.

• Journal of the Society of Naval Architects of Korea
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• v.61 no.1
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• pp.19-28
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• 2024

Environmental regulations are becoming more stringent in response to climate change, especially concerning marine pollution caused by ship emissions. Large ships are adjusting by integrating technologies to reduce pollutant emissions and transitioning to eco-friendly fuels such as low-sulfur oil and LNG. However, small ships face space constraints for installing LNG propulsion systems and the risk of power depletion with pure electric propulsion. Consequently, there's growing interest in researching hybrid propulsion methods that combine electricity and diesel for smaller vessels. Hybrid propulsion systems utilize diverse energy sources, requiring an effective method for evaluating their efficiency. This study proposes employing Bond graph modeling to comprehensively analyze energy dynamics within hybrid propulsion systems, facilitating better understanding and optimization of their efficiency. Modeling of the ship's energy system using Bond graphs will be able to provide a framework for integrating various energy sources and evaluating their effects.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.2
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• pp.114-120
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• 2012

Recently, integrated electric propulsion system has been vigorously adopted into naval vessels. To enhance effectiveness and efficiency of power management in these propulsion systems, this paper investigates necessity of energy storage devices and their operation strategies. By introducing the energy storage devices, engine can operate at higher efficiency point and accordingly costs for fuel and maintenance are significantly reduced. In addition, transient performance can also be improved with support of the devices and it leads to stable operation of shipboard power bus. To validate the proposal of this paper, computer simulation has been conducted with real load data of existing electric propulsion system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.443-444
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• 2009

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.577-587
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• 2004

A coaxial pulsed plasma thruster (PPT) with a Teflon cavity was designed, and its performance characteristics were examined varying stored energy, cavity length and capacitance. The PPT was tested as the entire system including the discharge circuit, and the results were explained with both the transfer efficiency and the acceleration efficiency. The transfer efficiency is defined as the fraction of energy in capacitors supplied into plasma, and the acceleration efficiency as the fraction of energy supplied into plasma converted to thrust energy. To estimate these efficiencies, the equivalent plasma resistance was defined and calculated using energy conservation during discharge. The equivalent plasma resistance proportionally increased with cavity length, and therefore the current peak increased with decreasing cavity length. The energy density calculated by the transfer efficiency was increased with decreasing cavity length. As a result, higher acceleration efficiency and lower transfer efficiency were obtained with shorter cavity length. Accordingly, there was an optimal cavity length for the thrust efficiency. The specific impulse and the impulse bit per unit stored energy ranged from 390 s and 50 $\mu$ Ns/J for a cavity length of 34 mm to 825 s and 11 $\mu$ Ns/J for a cavity length of 4 mm when the stored energy was fixed to 21.4J. Thus, it was showed that the performance of this PPT approached that of electromagnetic-acceleration-type PPT with decreasing cavity length. The PPT achieved thrust efficiencies of 10-12% at 21.4 J and 6-7% at 5.35 J at cavity lengths between 14 mm and 29 mm.

• Journal of Power System Engineering
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• v.15 no.2
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• pp.78-83
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• 2011

This paper aims at investigation some operating characteristics and energy usage efficiency of a induction motor and a BLDC motor considering electric propulsion system in a small ship based on battery source. At first, performance curves of discharge voltage from the battery and current from each motor according to the load variations were analyzed. Next, variations of motor torque and rotational speed versus load change at each motor were analyzed. Finally, efficiency of energy usage of the battery and available navigation distance were compared each other. Through some comparisons and analyses, it was cleared that the BLDC motor is more suitable for the motor of the electric propulsion system in small ships based on battery source. It is expected that the results can be used as useful data for design of the electric propulsion system with batteries.

• Proceedings of KOSOMES biannual meeting
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• 2018.06a
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• pp.175-175
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• 2018

• Journal of Power System Engineering
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• v.14 no.1
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• pp.27-33
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• 2010

We investigate some operation characteristics and energy efficiency of the BLDC motor system driven by different two types power conversion method depends on same battery source for applying to electrical motor propulsion system of a small ship. Also, we suggest an estimation manner of operating performances such as total running distance and operating speed of ships from basic discharge voltage characteristics of batteries. Through some experiments, direct power conversion was better than indirect method on the view point of energy efficiency and the voltage discharge characteristics could be used as important design factor for estimating operating performances of small ships driven by electrical motors.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.294-299
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• 2004

An assessment of a novel laser-electric hybrid propulsion system was conducted, in which a laser-induced plasma was induced through laser beam irradiation onto a solid target and accelerated by electrical means instead of direct acceleration only by using a laser beam. A fundamental study of newly developed rectangular laser-assisted pulsed-plasma thruster (PPT) was conducted. On discharge characteristics and thrust performances with increased peak current compared to our previous study to increase effects of electromagnetic forces on plasma acceleration. Maximum peak current increased for our early study by increasing electromagnetic effects in a laser assisted PPT. At 8.65 J discharge energy, the maximum current reached about 8000 A. Plasma behaviors emitted from a thruster in various cases were observed with an ICCD camera. It was shown that the plasma behaviors were almost identical between low and high voltage cases in initial several hundred nanoseconds, however, plasma emission with longer duration was observed in higher voltage cases. Canted current sheet structures were also observed in the higher voltage cases using a larger capacitor. With a newly developed torsion-balance type thrust stand, thrust performances of laser assisted PPT could be estimated. The impulse bit and specific impulse linearly increased. On the other hand, coupling coefficient and the thrust efficiency did not increase linearly. The coupling coefficient decreased with energy showing maximum value (20.8 ？Nsec/J) at 0 J, or in a pure laser ablation cases. Thrust efficiency first decreased with energy from 0 to 1.4 J and then increased linearly with energy from 1.4 J to 8.6 J. At 8.65 J operation, impulse bit of 38.1 ？Nsec, specific impulse of 3791 sec, thrust efficiency of 8 %, and coupling coefficient of 4.3 ？Nsec/J were obtained.